One common use for capacitors is in connection with the motors of air-conditioning systems. The systems often employ two capacitors, one used in association with a compressor motor and another smaller value capacitor for use in association with a fan motor. Air-conditioning systems of different BTU capacity, made by different manufacturers or being a different model all may use capacitors having different values. These capacitors have a finite life and sometimes fail, causing the system to become inoperative.
A serviceman making a service call usually will not know in advance whether a replacement capacitor is necessary to repair an air-conditioning system, or what value capacitor or capacitors might be needed to make the repair. One option is for the serviceman to carry a large number of capacitors of different values in the service truck, but it is difficult and expensive to maintain such an inventory, especially because there can be a random need for several capacitors of the same value on the same day. The other option is for the serviceman to return to the shop or visit a supplier to pick up a replacement capacitor of the required value. This is inefficient as the travel time to pick up parts greatly extends the overall time necessary to complete a repair. This is extremely detrimental if there is a backlog of inoperative air-conditioning systems on a hot day. This problem presents itself in connection with air-conditioning systems, but is also found in any situation where capacitors are used in association with motors and are replaced on service calls. Other typical examples are refrigeration and heating systems, pumps, and manufacturing systems utilizing compressors.
A desirable replacement capacitor would have the electrical and physical characteristics of the failed capacitor, i.e. it should provide the same capacitance value or values at the same or higher voltage rating, be connectable using the same leads and be mountable on the same brackets or other mounting provision. It should also have the same safety protection, as confirmed by independent tests performed by Underwriter Laboratories or others. Efforts have been made to provide such a capacitor in the past, but they have not resulted in a commercially acceptable capacitor adapted for replacing capacitors having a wide range of capacitance values.
U.S. Pat. Nos. 3,921,041 and 4,028,595 disclose dual capacitor elements in the form of two concentric wound capacitor sections. My U.S. Pat. No. 4,263,638 also shows dual capacitors sections formed in a wound capacitive element, and my U.S. Pat. No. 4,352,145 shows a wound capacitor with dual elements, but suggests that multiple concentric capacitive elements may be provided, as does my U.S. Pat. Nos. 4,312,027 and 5,313,360. None of these patents show a capacitor having electrical and physical characteristics necessary to replace any one of the variety of failed capacitors that might be encountered on a service call.
An effort to provide a capacitor with multiple, selectable capacitance values is described in my U.S. Pat. No. 4,558,394. Three capacitance sections are provided in a wound capacitor element that is encapsulated in a plastic insulating material. An external terminal lug is connected with one of capacitor's sections and a second external terminal lug is provided with a common connection to all three capacitor sections. Pre-wired fixed jumper leads each connect the three capacitive sections in parallel, and the pre-wired fixed jumper leads have a portion exposed above the plastic encapsulation. This permits one or two jumper leads to be severed to remove one or two of the capacitor sections from the parallel configuration, and thereby to adjust the effective capacitance value across the terminal lugs. The '394 patent suggests that further combinations could be made with different connections, but does not provide any suitable means for doing so.
Another attempt to provide a capacitor wherein the capacitance may be selected on a service call is described in my U.S. Pat. No. 5,138,519. This capacitor has two capacitor sections connected in parallel, and has two external terminals for connecting the capacitor into a circuit. One of the terminals is rotatable, and one of the capacitor sections is connected to the rotatable terminal by a wire which may be broken by rotation of the terminal. This provides for selectively removing that capacitor section and thereby reducing the capacitance of the unit to the value of the remaining capacitor. This capacitor provides a choice of only two capacitance values in a fluid-filled case with a cover incorporating a pressure interrupter system.
In another effort to provide a universal adjustable capacitor for AC applications, American Radionic Co., Inc. produced a capacitor having five concentric capacitor sections in a cylindrical wound capacitor element. A common lead was provided from one end of the capacitor sections, and individual wire leads were provided from the other ends of the respective capacitor sections. The wound capacitor element was encapsulated in a plastic insulating material with the wire leads extending outwardly from the encapsulating material. Blade connectors were mounted at the ends of the wire leads, and sliding rubber boots were provided to expose the terminals for making connections and for shielding the terminals after connections were made. Various capacitance values could be selected by connecting various ones of the capacitor sections in parallel relationship, in series relationship, or in combinations of parallel and series relationships. In a later version, blade terminals were mounted on the encapsulating material. These capacitors did not meet the needs of servicemen. The connections were difficult to accomplish and the encapsulated structure did not provide pressure interrupter protection in case of capacitor failure, wherein the capacitors did not meet industry safety standards and did not achieve commercial acceptance or success.
Thus, although the desirability of providing a serviceman with a capacitor that is adapted to replace failed capacitors of a variety of values has been recognized for a considerable period of time, a capacitor that meets the serviceman's needs in this regard has not heretofore been achieved. This is a continuing need and a solution would be a considerable advance in the art.